You're reading the documentation for a version of ROS 2 that has reached its EOL (end-of-life), and is no longer officially supported. If you want up-to-date information, please have a look at Jazzy.
Release Notes
This page should highlight the most important changes of the ros2_control framework in the iron release. If you are skipping a distribution update, make sure to read the release notes of all intermediate distributions.
These lists might not be complete, see the CHANGELOG.rst
files in the respective repositories for a full list of changes.
For necessary changes to your code for a version update, see the Migration Guides.